Java How to convert UTC milliseconds into UTC Date

Question

I have an int 1446159600 which is UTC/GMT date Thu, 29 Oct 2015 23:00:00 GMT. I tried to do conversion to the actual UTC date, but couldn't get it to work with Calendar, SimpleDateFormat, and Timezone classes. Can someone help me?

Answer 1

to;dr

Instant.ofEpochSecond ( 1_446_159_600L )

2015-10-29T23:00:00Z

Count From Epoch

You appear to have an integer count-from-epoch counting whole seconds with an epoch of Unix time, the first moment of 1970 in UTC.

The old date-time classes you reference are based on milliseconds. So multiply by 1,000.

java.time

Even better, avoid those old classes altogether. The new java.time framework in Java 8 and later is a vast improvement, supplanting those old classes. See Tutorial. These new classes have a resolution of nanoseconds, or 9 decimal places in a fraction of a second.

The Instant class (a moment on the timeline in UTC) even has a handy ofEpochSecond method, so no need to multiply by a thousand.

long wholeSecondsFromEpochInUtc = 1_446_159_600L;
Instant instant = Instant.ofEpochSecond ( wholeSecondsFromEpochInUtc );

That solves your Question in a one-liner.

Formatting

We can go further. Apply a time zone to that Instant to get a ZonedDateTime.

ZoneId zoneId = ZoneId.of ( "America/Montreal" );
ZonedDateTime zdt = ZonedDateTime.ofInstant ( instant , zoneId );
DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedDateTime ( FormatStyle.FULL ).withLocale ( Locale.CANADA_FRENCH );
String output = zdt.format ( formatter );

Dump to console.

System.out.println ( "instant (UTC): " + instant );
System.out.println ( "zdt: " + zdt );
System.out.println ( "output: " + output );

instant (UTC): 2015-10-29T23:00:00Z

zdt: 2015-10-29T19:00-04:00[America/Montreal]

output: jeudi 29 octobre 2015 19 h 00 EDT

Answer 2

// print the time in local time zone
        Date date = new Date(1446159600);
        System.out.println(date);

        // print UTC time 
        TimeZone utcTimeZone = TimeZone.getTimeZone("UTC");

        Calendar calendar = Calendar.getInstance(utcTimeZone);

        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(
                "EE MMM dd HH:mm:ss zzz yyyy", Locale.US);
        simpleDateFormat.setTimeZone(utcTimeZone);
        calendar.setTimeInMillis(date.getTime());

        System.out.println(simpleDateFormat.format(calendar.getTime()));

        //print in local time zone 
        //Because getTime method actully call new Date(long millsecond);

        /* public final Date getTime() {
                return new Date(getTimeInMillis());
            }*/
        System.out.println(calendar.getTime());

Answer 3

The timestamp seems to be in seconds while most java uses milliseconds so we have to multiply by 1000.

    long timestampMilliseconds = 1446159600*1000L;
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss z", Locale.US);
    simpleDateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
    String stringDate = simpleDateFormat.format(new Date(timestampMilliseconds));
    System.out.println(stringDate); // Thu, 29 Oct 2015 23:00:00 GMT

The L after 1000 is so that the multiplication is done as long values and the number does not overflow integer max value. You can use ((long)1446159600)*1000, 1446159600L*1000 or whatever to get the same effect. You can use TimeUnit.SECONDS.toMillis(1446159600) too.

Answer 4

Actually 1446159600 milliseconds is "Sat Jan 17 23:12:39 IST 1970". IST being my local time.

But, you can get the date associated using a Calendar object like follows.

    Calendar cal = new GregorianCalendar();
    cal.setTimeInMillis(1446159600 );
    System.out.println(cal.getTime());

And, the output in this happens to be "Sat Jan 17 23:12:39 IST 1970"

Also, if you want to convert the milliseconds to a date, you can use http://currentmillis.com/ It gives the date associated with the given millisecs.

Answer 5

Maybe I'm misunderstanding the problem, but this creates a Date from the current time in milliseconds:

public class DateTime
{
  public static void main (String[] args)
  {
    long time = System.currentTimeMillis ();
    System.out.println (time);
    Date date = new Date (time);
    System.out.println (date);
  }
}

which outputs:

1446191239738
Fri Oct 30 18:47:19 AEDT 2015

Answer 6

Check this code out:

    // Make a format for showing the date
    DateFormat dateFormat = new SimpleDateFormat("dd MMM, yyy", Locale.FRANCE);
    // Make a format for showing the time
    DateFormat timeFormat = new SimpleDateFormat("hh:mm a", Locale.FRANCE);

    // Get the current time in UTC (in milliseconds since 01 Jan 1970)
    Long currentUTCDate = Calendar.getInstance().getTimeInMillis();

    // Convert the current time from UTC to normal date
    Date currentDate = new Date(currentUTCDate);

    // Take the date only from currentDate object using the dateFormat we made before
    // and pass it to currentDateOnly String
    String currentDateOnly = dateFormat.format(currentDate);
    // Do the same with the time
    String currentTimeOnly = timeFormat.format(currentDate);

In this code we can distinguish three main different classes:
1. SimpleDateFormat(), which returns an object of type DateFormat
2. Calendar, whcih one of it methods is getTimeInMillis()
3. Date, which makes an object that can hold every detail about the time you gave it

Now:
. The getTimeInMillis() returns a number of type Long, which holds the current number of milliseconds since 01 Jan 1970.
We use this type of Time to make it easier for making calculations with dates.
. In Date class, we have a constructor that takes our Long number from getTimeInMillis() as a parameter, and returns for us an object of type Date that holds every detail of the Time we gave it in the constructor.
. Now we don't need all the details that our object currentDate holds, so we make a filter to take only date and time from the currentDate object, and to accomplish that we use objects of type DateFormat.
. Making an object of type DateFormat, we use SimpeDateFormat() constructor and we pass to it a parameter as a String of a specific pattern that we want to take from our currentDate object, for example ("dd MMM, yyy"), which is in our code:

DateFormat dateFormat = new SimpleDateFormat("dd MMM, yyy", Locale.FRANCE);

. Finally we take our currentDate object as a paremeter to our dateFormat.format() method, which will return to us a String of a filtered Date of the same pattern we gave it, which is in our example "dd MMM, yyy", and the result will look something like:
08 Sep, 2018